1. Field of the Invention
The invention relates generally to microwave generator frequency control and, more particularly, but not by way of limitation, it relates to an improved microwave energy tuning system for use with microwave liquid treating apparatus utilizing both incident and reflected microwave power 10 indications to effect continuous tuning of the microwave energy applied to an associated applicator structure.
2. Description of the Prior Art
The prior art includes a number of teachings that are directed toward automatic control and changing of the output frequency and/or phase of magnetron devices. U.S. Pat. No. 2,640,922 discloses apparatus for determining the deviation from a center frequency by measuring the voltage differences at two selected points in a standing wave pattern. This was a very early teaching which recognized the utility of a standing wave pattern for monitoring microwave frequency changes in a wave guide or transmission line system. U.S. Pat. No. 2,832,934 provided a teaching of a servo-controlled tuner that was effective to match a transmission line to a load using a control signal that is developed from the directional coupler in response to probe created reflections within the wave guide. This teaching relies upon the insertion of an auxiliary probe in order to obtain an analytic signal which is used as the correction indicator.
U.S. Pat. No. 3,617,953 was directed to a microwave impedance matching system that included a directional coupler for sensing only reflected energy. The system used two phase shifters in separate control loops with respective microwave probe sensors to sense and match the real and imaginary parts of wave guide admittance. Finally, U.S. Pat. No. 3,742,394 covered a microwave tuning system with two probes sensing the standing wave pattern and a servo controlled tuning probe mounted on a slidable carriage to maintain maximum energy transfer in an associated microwave applicator.